The present invention relates generally to gas turbine engines, and more specifically to a starter controller and a method used to control the speed of the gas turbine engines during start-up.
A gas turbine engine typically includes a compressor stage, a combustor stage, and a turbine stage. The compressor stage compresses air provided at a forward end of the gas turbine engine and provides the compressed air to the compressor stage. Nozzles within the compressor stage add fuel to the compressed air. The compressed air/fuel mixture is ignited within the combustor and the resulting exhaust from the combustion generates thrust toward the aft end of the gas turbine engine. The exhaust is provided to the turbine stage, which extracts energy from the exhaust to provide the motive force necessary to power the compressor stage, such that the gas turbine engine is self-sustaining.
To start a gas turbine engine, a starter motor is used to provide motive force to the shaft connecting the compressor stage to the turbine stage. The starter motor is used to increase the speed of the compressor stage to a point at which the compressed air provided to the combustor stage results in a fuel/air mixture that is suitable for ignition (commonly referred to as ‘light-off’). Typically, light-off occurs at approximately 10-20% of the operating speed of the gas turbine engine. Following light-off, the starter motor continues to provide torque to the gas turbine engine until the engine reaches approximately 50-60% of the engine's operating speed. At this point, the gas turbine engine is self-sustaining (i.e., the power generated by the gas turbine is sufficient to power the compressor stage) such that the gas turbine engine does not require motive force from the starter motor.
To initiate light-off, it is therefore important to control the speed of the gas turbine engine to provide the proper fuel/air mixture to the combustion chamber.